COMPARISON OF THE EFFECT OF FILTER DESIGNS ON THE TOTAL HARMONIC DISTORTION IN THREE-PHASE STAND-ALONE PHOTOVOLTAIC SYSTEMS

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1 O. 0, NO., NOEMBER 05 ISSN ARPN Journl of Engineering nd Applied Sciences Asin Reserch Pulishing Network (ARPN). All rights reserved. OMPARISON OF THE EFFET OF FITER ESIGNS ON THE TOTA HARMONI ISTORTION IN THREE-PHASE STAN-AONE PHOTOOTAI SYSTEMS Yew Weng Ken, Png Siew Yong, Agileswri Rmsmy nd. K. Rmchndrmurthy Power Qulity Reserch Group, eprtment of Electricl Power Engineering, University Teng Nsionl, Kjng, Mlysi E-Mil: ABSTRAT The world hs turned their ttention to renewle energy with the incresing demnd of power supply nd the limited source of fossil fuel. In Mlysi, solr P energy is growing stedily s the sunlight is esily ville throughout the yer. As more solr P system eing instlled, stnd-lone opertion is eing looked into to ring solr P to rurl res. However, in stnd-lone opertions there is no voltge support from the grid which will led to hrmonic prolems. Pssive filter is one of the methods used to mitigte the hrmonic issues in stnd-lone system. This pper focuses on the design of pssive filters nd the effects of the filter on the totl hrmonic mitigtion in 8kW three-phse stnd-lone P system re compred. The design of the proposed filters is vlidted y simultion results in PSA softwre. The simultion results show tht the doule tuned filter design is le to meet the TH nd individul hrmonic limit stndrds etter s compred to the single tuned filter nd filter design. Keywords: doule tuned filter, totl hrmonic distortion, photovoltic system, stnd-lone, pssive filter. INTROUTION Over the lst few yers, implementtion of solr P in Mlysi hve een rising stedily with the governments inititive of the Feed-in-triff. Most Solr P systems instlled re eing connected to the utility grid either through commercil or residentil where there is strong inerti support provided y the ntionl grid system []. As more solr P system eing instlled, stnd-lone opertion is eing looked into to ring solr P to rurl res []. However, in stnd-lone opertions there is no voltge support from the grid for n A coupled system [3]. This will led to power qulity prolems when the system is operted in stnd-lone mode. Hrmonics re inevitle in stnd-lone P system s power converters re widely used for the opertion of the system. Hrmonics in stnd-lone P system re generted from the switching of the diodes/trnsistors in the inverter. These hrmonics my ffect the opertion of the inverter or the stnd-lone P system resulting in low power qulity. For stnd-lone P systems to e le to supply high qulity power, the hrmonic level of the current supplied must meet the stndrd set y the interntionl odies nd cn e found in IEEE 59-99, ER G5/4, IE , nd IE [4, 5, 6, 7]. Out of the mny stndrds, Mlysi follows the IE stndrds set y the governing commission. Pssive filter is one of the methods for hrmonics mitigtion in system. This pper focuses on the design of pssive filters nd the effects of the filter on the totl hrmonic distortion re compred. Among the types of pssive filters re single tuned filters nd doule tuned filters. A single tuned filter is mde from series of R components while the doule tuned filter hs mny topologies such s the series-prllel R components or prllel-prllel R components. The function of single tuned filter is to filter out specific frequency y creting low-impednce pth to ground. The dominnt hrmonics currents will flow out of the lod resulting in lower totl hrmonic distortion (TH). A single tuned filter cn e tuned on specific frequency y mking the inductive nd cpcitive cncel ech other out. The most dominnt frequency is usully selected to otin etter hrmonic mitigtion from the single tuned filter. The doule tuned filter design is n improvement from the single tuned filter design. It is designed to improve the performnce of the single tuned filter [7]. This pper focuses on the design of pssive filters nd the effects of the filter on the totl hrmonic mitigtion in 8kW three-phse stnd-lone P system re compred. The design of the proposed filters is vlidted y simultion results in PSA softwre. This pper is orgnized in five sections. In section II, the modelling of the solr P is discussed. Section III discusses the vrious filter designs for hrmonic mitigtion. The results nd simultion from the design is discussed in Section I. Section concludes nd summrizes the key points of the pper. MOEING OF STAN-AONE P SYSTEM The stnd-lone P system rted t 8kW is modeled in PSA using n rry of monocrystlline P cells. The P cells re then connected to / uck converter controlled y MPPT to otin the mximum power output from the P cell. This is followed y three phse inverter. To mitigte the hrmonics from the three phse inverter output, filter must e inserted fter the inverter. Figure- shows the generl lock digrm of the stnd-lone P system. 999

2 O. 0, NO., NOEMBER 05 ISSN ARPN Journl of Engineering nd Applied Sciences Asin Reserch Pulishing Network (ARPN). All rights reserved. Figure-. Block digrm of the stnd-lone P system. P cell A solr cell is semiconductor device tht sors light to generte electricity. P cell is rrnged in series nd prllel to mtch the system current nd voltge requirement [8, 9]. The simplest modeling of solr cell is uilt from current source in prllel with diode, shunt resistor, R sh, nd in series with resistor R s s shown in Figure-. Figure-. Model of P cell. From the clcultion for the equivlent circuit of the solr cell, the output current I cn e clculted s: I I I I () SH I is the current generted y the solr cell. I is the current flowing though the diode which relies on the solr cell temperture. I SH is the current flowing in the equivlent shunt resistnce of the solr cell. [0] I SH R I () S ( RS I) (3) R SH q I I s[exp( ) ] (4) nkt n = diode idelity fctor ( for n idel diode) = voltge cross the diode q = elementry chrge :.60 X 0-9 K = Boltzmnn s constnt :.38 X 0-3 T = solute temperture in Kelvin scle I = rted short circuit current of solr cell s MPPT nd / uck converter / Buck converter is chosen ecuse it hs higher efficiency thn other converters nd it is le to step down the higher voltge from the solr rry. This is designed together with the Mximum Power Point Trcker (MPPT) controller in this stnd-lone system. With the help of the / Buck converter nd MPPT, mximum power from the solr rry cn e otined. Incrementl onductnce (I) method is selected for this MPPT [, 3] Three phse inverter The function of the Three Phse Inverter is used to convert the power from the / converter to 3 Phse A power to feed the lods. Sine Wve Pulse Width Modultion (SPWM) method is used to crete the switching signl nd inject to the IGBT of the inverter. The switching signl is creted y compring the modulting signl (sin wve) with the crrier signl (tringulr wve). FITER ESIGNS FOR HARMONI MITIGATION The output voltge nd current of inverter usully contin lot of hrmonic components s result from the switching signls. Besides choosing higher switching frequency to reduce the hrmonic, the high frequency hrmonic contents cn e filtered y using filter. Hence, filter is designed nd used to filter out the high frequency hrmonic contents in the inverter output power. Pssive filter is one of the methods for hrmonics mitigtion in system. In this reserch, filter, single tuned filter nd doule tuned filter re designed nd the effects of the filter on the totl hrmonic mitigtion re compred. The preliminry results from the stnd-lone P system with filter re used s reference to design the single tuned nd doule tuned filter. filter Figure-3. filter model. filter is widely used to filter out the hrmonics in the inverter output power to generte clener output power. The filter is connected etween the inverter nd the lod in the stnd-lone P system. The filter inductnce vlue is designed such tht the current ripple cross the inductor is limited to 5% [4]. The model of the filter is shown in Figure

3 O. 0, NO., NOEMBER 05 ISSN ARPN Journl of Engineering nd Applied Sciences Asin Reserch Pulishing Network (ARPN). All rights reserved. i p (5) 6 f i s ripple, pek ripple pek 5% I rted, (6) oule tuned filter To design doule tuned filter, second n-th order hrmonic must e determined to improve on the single tuned filter design. The model of the doule tuned filter is shown in Figure-5. p = rms phse voltge f s = inverter switching frequency The filter cpcitnce vlue is then clculted from the resonnce eqution s given in: (7) ( f 0 ) f 0 = cut-off frequency Single tuned filter The single tuned filter cn e designed if the dominnt hrmonic is known. In single tuned filter, n inductor, is dded in series with the cpcitor to crete low pth impednce line t the dominnt hrmonic frequency. From this design, the inductive nd cpcitive rectnce from nd will cncel ech other out t the n-th order frequency. The model of the single tuned filter is shown in Figure-4. Figure-5. oule tuned filter model. For the design of the doule tuned filter, secondry set of inductor nd cpcitor, nd must e clculted using eqution (8) t the second n-th order hrmonic to crete nother zero impednce pth. The first set of inductor nd cpcitor re used for nd [5]. After otining the vlues for,,, nd, the min inductors nd cpcitors in the doule tuned filter design re clculted with (9) to () s elow:- ( )( ) ( ) (9) (0) () ( ( ) ) ( ) () Figure-4. Single tuned filter model. The inductnce is clculted from eqution (8). (8) ( f ) r = resonnce frequency From the design of the single tuned filter, the output totl hrmonic distortion should e lower compred to the initil filter. If the TH does not decrese, the filter should e redesigned with different dominnt hrmonic. SIMUATION RESUTS AN ISUSSION Simultion is crried out to nlyze the qulity of the output voltge nd current when the system is connected with n filter, single tuned filter nd doule tuned filter. The current individul hrmonic content for ech simultion is mesured nd compred with the interntionl stndrds. The results discussed in this pper pplies the Stndrd Test ondition (ST) prmeters which re 000W/m nd 5o. The focus of the nlysis will e on the TH voltge nd current nd individul hrmonic content ccording to the interntionl stndrd IE s shown in Tle-. 99

4 O. 0, NO., NOEMBER 05 ISSN ARPN Journl of Engineering nd Applied Sciences Asin Reserch Pulishing Network (ARPN). All rights reserved. Tle-. urrent distortion limits (IE ) [7]. filter To determine the prmeters for the filter the vlues re clculted from eqution (5), (6) nd (7). The prmeters used for nd re shown in Tle-. Tle-. filter prmeters. The results from the simultion of the stnd-lone P system with the filter is shown in Figure-6. Figure-6. Simultion results of filter () Output voltge grph () Output current grph urrent individul hrmonic profile. From this simultion, it ws found tht the dominnt hrmonics is found on the 5th hrmonic of the output current t 3.5% while the nd hrmonic of the output current is found t %. The totl hrmonic distortion (TH) of the current is 3.5%. According to the IE stndrd, the 5th hrmonics result is very close with the 5th hrmonic stndrd which is t 4% while the nd hrmonics result orders on the nd hrmonic stndrd limit t %. These results re not idel s it is too close to the order. As this simultion is simulted t ST, the intermittent nture of the solr irrdince will hve smll effect on the output hrmonics in prcticl environment. Therefore, the hrmonics level must e lowered in order to keep the system within the limits of the IE stndrd. Single tuned filter From the preliminry results, the dominnt hrmonic is used to clculte the filter prmeters of the single tuned filter design ccording to eqution (8). The single tuned filter is designed to filter the 5th order hrmonic s it is the most dominnt hrmonic from the result with the filter. The filter prmeters used re shown in Tle-3. () Tle-3. Single tuned filter prmeters. The result of the simultion of the single tuned filter is shown in Figure-7. () 99

5 O. 0, NO., NOEMBER 05 ISSN ARPN Journl of Engineering nd Applied Sciences Asin Reserch Pulishing Network (ARPN). All rights reserved. Tle-4. oule tuned filter prmeters. () The result of the simultion of the doule tuned filter is shown in Figure-8. () () Figure-7. Simultion results of Single tuned filter () Output voltge grph () Output current grph urrent individul hrmonic profile. () From the single tuned filter results in Figure 7, it cn e seen tht the 5th order hrmonics hs een reduced significntly compred to the stnd-lone P system with filter. Although the TH of the system decresed with the single tuned filter, the nd order hrmonics however, hs incresed nd it is now.% which is ove the limit of %. oule tuned filter The dominnt hrmonics from the results from the filter nd single tuned filter re used to clculte the filter prmeters of the doule tuned filter design ccording to eqution (9) to (). The doule tuned filter is designed to filter oth the nd order nd 5th order hrmonics. The filter prmeters used re shown in Tle-4. Figure-8. Simultion results of oule tuned filter () Output voltge grph () Output current grph urrent individul hrmonic profile. This prolem is rectified in the doule tuned filter nd cn e seen in the results. With the design of the doule tuned filter, the nd order hrmonics is reduced to 993

6 O. 0, NO., NOEMBER 05 ISSN ARPN Journl of Engineering nd Applied Sciences Asin Reserch Pulishing Network (ARPN). All rights reserved. only 0.08%. The output TH of the stnd-lone P system with the doule tuned filter is reduced to 0.5%. This generted smooth sine wve t the output current nd is le to provide high qulity power to the lods. omprison of the effect of filter designs on the totl hrmonic distortion The effect of the filter designs on the Totl Hrmonic istortion (TH) of the output current of the stnd-lone P system re compred. When the system is simulted without ny filter, the system gives TH of 0.35%. This shows tht there is high hrmonic level in stnd-lone P system when there is no filter to filter the high frequency hrmonic contents. Thus, with the filter designs, the TH level is reduced to 3.5%,.% nd 0.5% with, single tuned filter nd doule tuned filter respectively. The overll comprison of TH results of the stnd-lone P system with the, single tuned nd doule tuned filter designs nd without filter re shown in Tle-5. Tle-5. TH results without filter, with filter, with single tuned filter nd doule tuned filter. The Totl Hrmonic istortion of Stnd-lone P system without filter, with filter, with single tuned filter, nd with doule tuned filter re shown in Figure-9. (d) Figure-9. Totl Hrmonic istortion of stnd-lone P system () without filter () with filter with single tuned filter (d) with doule tuned filter. ONUSIONS This pper hs presented comprison of the effect of the filter designs on the current TH in 8kW stnd-lone P system. The result otined from the PSA simultion shows tht the doule tuned filter cn effectively reduce urrent TH from 0.35% to 0.5%. This shows the importnce of designing doule tuned filters for hrmonic mitigtion in future stnd-lone P systems. However, this design depends hevily on the udget ville to construct the system s dditionl costs hve to e incurred to include the extr components of the doule tuned filter. REFERENES () [] E.Koutroulis, K.Klizkis nd N.. oulgris. 00. evelopment of microcontroller-sed, photovoltic mximum power point trcking control system. IEEE Trnsctions on Power Electronics. ol. 6, No., pp [] N. W. nden Eynde, S.howdhury, nd S.P.howdhury. 00. Modeling nd simultion of stnd lone photovoltic plnt with MPPT feture nd dedicted ttery storge. IEEE Power nd Energy Society Generl Meeting, pp. 8, Minnepolis, USA. () [3] A.hikh nd A.hndr. 0. oltge nd frequency controller for stndlone P system with ttery storge element. IEEE

7 O. 0, NO., NOEMBER 05 ISSN ARPN Journl of Engineering nd Applied Sciences Asin Reserch Pulishing Network (ARPN). All rights reserved. [4] IEEE Std Recommended Prctices nd Requirements for Hrmonic ontrol in Electric Power Systems. [5] ER G/54. Engineering Recommendtion G5/4. [6] IE/TR Assessment of emission limits for the connection of distortion instlltions to M, H nd EH power systems. [7] Interntionl Electrotechnicl ommission, IE 677, Second Edition 004. Photovoltic (P) systems hrcteristics of the utility interfce. [8] Shivnnd Pukhrem. 03. A photovoltic pnel model in Mtl/Simulink. Renewle Energy System. [9] Anc.Hnsen, Poul Sorensen, rs H. Hnsen nd Henrik Bindner Models for stnd-lone P system. Riso Ntionl ortory, Roskilde. [0] Moun Tli, Adelltif Odi, Adelkrim Elfjri nd Youssef Errmi. 04. Pssive filter for hrmonics mitigtion in stndlone P system for non liner lod. The nd Interntionl Renewle nd Sustinle Energy onference Qurzzte. Qurzzte, Morocco. [] M.A Frht, H.M.B Metwlly, Ahmed d-elfth Mohmed. 0. Optiml choice nd design of different topologies of - converter used in P systems t different climtic conditions in Egypt. Renewle Energy. pp [] G.J Kish, J.J ee nd P.W.ehn. 0. Modeling nd control of photovoltic pnels utilizing the incrementl conductnce method for mximum power point trcking. IET Renewle Power Genertion. pp [3] Mhmed Rehi, Ali Bentillh, Mrouk Sellm nd Boufeldj Kdri. 03. omprtive study of MPPT controllers for P system implemented in the southwest of Algeri. TerrGreen 3 Interntionl 03. pp [4] B.H. Yong nd.k. Rmchndrmurthy. 04. Hrmonic mitigtion of grid connected 5MW solr P using filter. EAT 04. [5]B.H. Yong nd.k. Rmchndrmurthy. 04. oule tuned filter design for Hrmonic mitigtion in grid connected solr P. PEON